The invention relates to a device for preventing uncontrolled acceleration of an elevator car of an elevator installation both in the upward direction and in the downward direction.
In elevator installations an elevator car is usually connected to a counterweight by a rope over a traction sheave which transmits driving action to the car. To ensure that in the case of a functional fault such as, for example, failure of the driving device, the elevator car is not accelerated in uncontrolled manner by the difference in weight between the elevator car and the counterweight, a corresponding safety device is prescribed. Because the counterweight is usually designed so that when the elevator car is carrying half the permitted rated load there is a state of equilibrium, uncontrolled acceleration can occur in both the downward direction and in the upward direction depending on whether the elevator car is carrying more or less than half the permitted rated load. The safety device must therefore respond both when there is uncontrolled acceleration in the downward direction and in the upward direction.
A device for preventing uncontrolled acceleration of an elevator car in an elevator installation is known, for example, from EP 0 440 839 A1. The safety device according to that printed publication responds both in the case of an uncontrolled acceleration in downward direction and an uncontrolled acceleration in upward direction. To detect the uncontrolled acceleration of the elevator car, a governor rope is provided which is independent of the traction rope and which runs endlessly over an upper return pulley and a lower return pulley. Provided on the lower return pulley is a weight to keep the governor rope constantly taut. Located on the upper return pulley is an overspeed governor. The elevator car is connected to the governor rope via an actuating lever which serves as a tripper and which, when the elevator car is running undisturbed, is constantly transported with the latter so that the speed of rotation of the upper return pulley is proportional to the speed of the elevator car. The overspeed governor detects the speed of rotation of the upper return pulley and is so designed that, when a limit speed of rotation of the upper return pulley is exceeded, the overspeed governor blocks the latter so that the upper return pulley is brought to rest. Because the governor rope is still transported by the elevator car, the governor rope slips over a groove provided in the upper return pulley and thereby experiences a frictional resistance which causes a tripping force to be transmitted via the governor rope to the tripping mechanism of the braking device. Thereupon, the braking device responds and presses brake shoes against a guiderail of the elevator installation so that the elevator car is braked and held. Different brake shoes are provided for braking/holding the elevator car in the downward direction and the upward direction respectively.
As shown in detail below by means of FIGS. 10 and 11, the force which acts on the fall of the governor rope connected to the tripper depends to a substantial extent on whether the elevator car is moving in a downward or an upward direction. Stated simply, if the elevator car is moving upward, the fall of the governor rope connected to the tripper pulls on the weight of the lower return pulley directly. On the other hand, if the elevator car is moving downward, the fall of the governor rope connected to the tripper pulls on the weight of the lower return pulley via the stationary upper return pulley so that in this case the force acting on the rope fall connected to the tripper is substantially increased by friction.
The dimensions of the safety device, particularly of the weight connected to the lower return pulley and of the geometry of the slot provided on the upper return pulley, over which the governor rope is pulled when the upper return pulley is stationary, must therefore be based on the braking operation of the elevator car moving in the upward direction because the tripping force for this case is lower. On the other hand, this also means that the tripping force when the elevator car is moving in a downward direction becomes so large that considerable problems arise with the dimensioning of the governor rope and of the tripper of the braking device, because the governor rope and the tripper must withstand this very high tripping force in the downward direction.
In EP 0 440 839 A1 the suggestion is made of arranging a compensation spring in the governor rope above the tripper. However, this compensation spring increases even further the tripping force in the downward direction, which is already too high anyway, and is therefore disadvantageous.
The objective of the invention is to create a device for preventing uncontrolled acceleration of an elevator car of an elevator installation in which the tripping force transmitted to the tripper of the braking device is limited.
According to the invention, it is proposed to connect the tripper of the braking device with the governor rope via a slipping connection so that the governor rope slips on the slipping connection if a force is transmitted from the governor rope to the tripper of the braking device which is substantially greater than the tripping force required to trip the braking device. By means of the proposed solution according to the invention, the maximum tripping force which is transmitted is limited, and the tripper of the braking device and the governor rope are thereby protected against overloading. In this manner, the components of the device can be so designed that on the one hand a tripping force is generated sufficient to trip the tripper of the braking device with certainty and thereby arrest an acceleration of the elevator car in the upward direction, but so that on the other hand the tripping force when arresting the elevator car in the downward direction is limited, which prevents overloading the tripper and governor rope.
The slipping connection can be so adjusted that the governor rope only slips on the slipping connection when the elevator car is braked in the downward direction. When the elevator car is braked in the upward direction, the governor rope then slips as hitherto over the stationary upper return pulley without activating the slipping connection according to the invention. Because a much larger force acts on the governor rope when braking the elevator car in the downward direction than when braking in the upward direction, it is sufficient for the slipping connection to slip in the downward direction. The slipping connection can be set with some margin of safety above the tripping force required to trip the braking device.
The slipping connection can be arranged immediately below the rope connector that connects the free ends of the governor rope to each other.
The slipping connection consists preferably of a base plate and a pressure plate which presses against the base plate with a specified compressive force, the governor rope being gripped between the base plate and the pressure plate. To generate the compressive force there is at least one tension screw which passes through and beyond a drilled hole of the pressure plate and can be screwed into a thread of the base plate. The depth to which the screw can be screwed into the thread, and therefore the compressive force, is limited by a tightening stop.
The compressive force can be generated by a compression spring compressed between the base plate and a projection of the tension screw, the compression spring consisting preferably of several cup springs arranged in a stack. The tightening stop can take the form of a sleeve surrounding the tension screw.
The governor rope is preferably guided in a groove in a surface of the base plate and/or the pressure plate which has a preferably triangular cross section. At the ends of the base plate and of the pressure plate the groove opens out into an area which preferably opens out both in the direction of the surface and perpendicular to the surface of the base plate and pressure plate respectively. The tripper of the braking device is fastened to either the pressure plate or the base plate.